Method and apparatus for detecting inconsistent control information in wireless communication systems

ABSTRACT

In order to support low latency and bursty internet data traffic, the 3GPP LTE wireless communication system uses dynamic allocation. To keep the allocation overhead lower, the system is designed such that the client terminal must perform a number of decoding attempts to detect resource allocations. During course of the decoding attempts a false resource allocation may be decoded by the client terminal. The false detection may lead to multiple issues for the performance efficiency of the client terminal and the overall communication system. A method and apparatus are disclosed than enable the detection of false resource allocation. This in turn improves the performance and efficiency of the client terminal and the wireless communication system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of the filing date of U.S.Provisional Application No. 61/760,167 filed Feb. 4, 2013 and entitled“METHOD AND APPARATUS FOR DETECTING INCONSISTENT CONTROL INFORMATION INLTE DOWNLINK CONTROL CHANNEL,” the entire disclosure of which is herebyexpressly incorporated by reference herein.

BACKGROUND OF THE INVENTION

The present invention relates generally to wireless communicationsystems and, more particularly, to mobile station receiver architecturesand methods that employ decoding multiple hypotheses such as in case of3rd Generation Partnership Project (“3GPP”) Long Term Evolution (“LTE”)wireless communication system.

As shown in FIG. 1, a wireless communication system 10 compriseselements such as a client terminal or mobile station 12 and basestations 14. Other network devices which may be employed, such as amobile switching center, are not shown. As illustrated, thecommunication path from the base station (“BS”) to the client terminaldirection is referred to herein as the downlink (“DL”) and thecommunication path from the client terminal to the base stationdirection is referred to herein as the uplink (“UL”). In some wirelesscommunication systems the client terminal or mobile station (“MS”)communicates with the BS in both DL and UL directions. For instance,this is the case in cellular telephone systems. In other wirelesscommunication systems the client terminal communicates with the basestations in only one direction, usually the DL. This may occur inapplications such as paging.

Most wireless communication systems have an overhead in terms ofmanaging and controlling the wireless link between the network and theclient terminal. A number of beacon signals may need to be transmittedby the base station that enables the client terminal to detect the basestation and synchronize to it. For example, in LTE wirelesscommunication system the Primary Synchronization Signal (“PSS”), theSecondary Synchronization Signal (“SSS”), and Physical Broadcast Channel(“PBCH”) are used to enable the client terminal to detect andsynchronize to the base station. Even after the client terminal detectsand synchronizes with the base station, it needs additional informationabout the detailed structure of the channel and various parametersrequired for communication with the base station in both DL and UL. Thisinformation is generally referred to as “System Information.” Dependingon the particular wireless communication system, the base station maytransmit the System Information in one or more smaller independent unitsof information.

Even after the client terminal has detected the base station,synchronized to it and had decoded the System Information, it does nothave any specific resources allocated to it for communication. For thispurpose, it has to first transmit a signal in UL to request resources inDL, UL, or both. In many wireless communication systems, multiple clientterminals use the same resources for communication. The base stationmanages the overall allocation of the resources to the multiple clientterminals contending for the same shared channel. While making resourceallocation decisions, the base station considers a number of factorssuch as the required bit rate, latency, quality of service required, biterror rate, channel conditions, the loading of the cell in terms ofnumber of active users, etc. Furthermore, these factors varycontinuously and the base station adapts its decisions dynamically.

Conventional wireless communication systems are primarily used for voicecalls and text messaging. The resource allocation for a voice can bedone once and then it does not change for a relatively long time. Forexample, average phone call duration may be in the order of minutes.Similarly, text messaging may be much less frequent. The latency inallocation of resources for setting up a voice call is usually in theorder of several seconds. This latency is generally acceptable to theusers since it is a onetime latency during the call setup. After thecall is setup the allocated channel resources are dedicated to the userfor the duration of the call. Another part of the resource allocation isthe overhead incurred in the process of allocating the resources. Forexample, number and size of control messages required to establish aphone call may be significant. However, the call setup overhead due tocontrol message is a small percentage of the duration of the call sincethe overhead is incurred only once per call.

Over the years, the use of the internet has increased over the wirelesscommunication networks. Normally the traffic pattern of internet usageis very bursty, e.g., the request for resources comes very frequentlybut each request is only for a short duration of time. Under suchtraffic conditions the latency of several seconds in the conventionalwireless communication systems may not be acceptable. Therefore, onerequirement is to have a resource allocation method that can allocateresources with low latency. Another requirement is that the allocationof the resources must incur low overhead since the allocation, releaseand reallocation of resources occur much more frequently.

The LTE wireless communication system is designed for low latency andhigh throughput applications. Examples of such applications include theweb browsing, mobile online gaming, video calls, media streaming, etc.Supporting such applications requires the allocation of resources in adynamic manner. This is in contrast with respect to the previousgeneration wireless communication systems that are designed forallocations that do not change for tens of seconds and even minutes andhours. In LTE wireless communication system, the resource allocation maychange once every millisecond.

The potential penalty for such dynamic resource allocation may be thatthe overhead for allocating the resources is incurred every millisecond.To keep the overhead of resource allocation low while keeping theresource allocation dynamic and the latency low, the LTE wirelesscommunication system employs several techniques.

The LTE wireless communication system employs Orthogonal FrequencyDivision Multiple Access (“OFDMA”) technology in the DL air interface.The basics of OFDMA are described in “4G LTE/LTE-Advanced for MobileBroadband” by Dahlman, Erik, et al., copyright 2011 and published byAcademic Press, MA, the entire disclosure of which is hereby expresslyincorporated by reference herein. The high level structure of the LTE DLair interface, as described in 3GPP TS 36.211: “Evolved UniversalTerrestrial Radio Access (“E-UTRA”); Physical channels and modulation,”is shown in FIG. 2. The air interface consists of series of frames of 10ms each and each frame consists of 10 subframes with 1 ms per subframe.As shown in FIG. 3 each subframe in turn consists of 12 or 14 OFDMsymbols depending on the length of Cyclic Prefix (“CP”) used. The FIG. 3shows the structure for Normal CP with 14 OFDM symbols per subframe forthe case of 10 MHz channel bandwidth with 50 Resource Blocks (“RBs”).FIG. 3A focuses on certain subframes from FIG. 3 for clarity purposes.

The first few OFDM symbols of each subframe are used for control channelpurposes and it is called Control Region as shown in FIG. 3. A controlchannel, called Physical Downlink Control Channel (“PDCCH”) is designedfor the purpose of dynamic resource allocation. The payload datadescribing the resource allocation information that is transmitted usingPDCCH is called Downlink Control Information (“DCI”). The DCI describesthe allocation of the resources in the remaining portion of the subframecall Data region.

The PDCCH is transmitted within the control region of each subframe. Thenumber of OFDM symbols used for the control region may vary from onesubframe to another. The actual number of OFDM symbols used for asubframe is given by another control channel called Physical ControlFormat Indicator Chanel (“PCFICH”). The PCFICH is always transmitted inthe first OFDM symbol of each subframe. The number of control symbols ineach subframe is at least one OFDM symbol. Each PDCCH allocatesresources for one client terminal in either DL or UL. Therefore, theremay be multiple PDCCHs in the control region.

In LTE wireless communication systems the base station is referred asEnhanced Node B (“eNB”). One of the requirements from eNB in LTEwireless communication systems is the flexibility in addressing (sendingresource allocation to) a particular client terminal through the PDCCH.This flexibility in turn requires the client terminal to search all thepossible PDCCH candidates within different parts of the control regionin each subframe, as shown in FIG. 3, for possible resource allocationto it. In any given subframe, there may or may not be any resourceallocation for a particular client terminal. The allocation for DL andUL are provided separately since the internet traffic pattern in generalmay be asymmetric. Therefore, in a single subframe there may be zero,one or two PDCCHs transmitted by the base station to a particular clientterminal. In some special conditions, there may be more than two PDCCHstransmitted to a particular client terminal in a single subframe.

To keep the allocation overhead low, the PDCCH may be transmitted withdifferent level of Forward Error Correction (“FEC”). This is referred toas Aggregation Level (“AL”) in LTE wireless communication systems.Depending on the expected signal conditions of the client terminal towhich the PDCCH is transmitted, the base station may dynamically use adifferent AL. However, the client terminal may not be a priori aware ofthe AL used by the base station. The AL used for different clientterminals may be different. A Control Channel Elements (“CCE”) consistsof 72 transmission bits (coded bits after FEC) and it is a basicallocation unit for PDCCH transmission within a subframe. Eachaggregation level uses one or more CCEs within the control region of asubframe. There are total of four different aggregation levels used inLTE wireless communication systems as shown in FIG. 4, employing 1, 2,4, and 8 CCEs with 72, 144, 288 and 576 transmission bits respectively.

In LTE wireless communication systems different formats for the DCImessages are used for handling different allocation requirements. Forexample, DL allocation and UL allocation messages may have differenttypes of information. In LTE wireless communication systems differentmulti-antenna transmission modes are used. Depending on the particulartransmission mode used the type and length of the DCI messages may vary.At any given time, a UE (user equipment) is required to decode DCImessages of at most two possible different lengths.

Considering all the above factors, the PDCCH AL, the length of the DCImessage and all the possible PDCCHs that may be transmitted by the basestation, the client terminal has to perform PDCCH decoding with a numberof different combinations. This is often referred to as blind PDCCHdecoding.

In LTE wireless communication systems different UEs are identified usingvarious identities known Radio Network Temporary Identifier (“RNTI”)which is unique within a cell. There are some RNTIs that are broadcasttype which address all the UEs in a cell whereas there are other RNTIsthat address a particular client terminal. Each client terminal isassigned a unique RNTI within the cell when it first camps on a cell. Ina PDCCH, a particular client terminal is addressed by the eNB by usingthe RNTI for that client terminal. However, in order to keep theoverhead low, the RNTI is not explicitly added to the DCI payload.

A concept of search space is used in LTE wireless communication systemsto reduce the number of PDCCH candidates that a client terminal mustdecode in each subframe. The search space is divided into two parts:Common Search Space (“CSS”) and UE Specific Search Space (“UESSS”). ThePDCCHs with broadcast RNTIs may be transmitted only in the CSS whereasthe PDCCH with UE specific RNTI may be transmitted in either the CSS orUESSS. The CSS is common to all the UEs that are camped on a cell. TheUESSS is derived from the UE specific RNTI. Within the control region ofeach subframe, the UE only searches within the CSS and its UESSS forpossible PDCCHs being transmitted to it. The specific CCEs to which aparticular PDCCH is mapped to is a function of the search space,aggregation level and the RNTI of the UE in case of UESSS. For the CSS,the PDCCHs are always mapped to the first 16 CCEs as shown in FIG. 5.The mapping of the UESSS PDCCH candidates depends on its RNTI and anexample of that is shown in FIG. 6. The summary of the PDCCH candidatesa UE is required search under normal operation is summarized in thetable contained in FIG. 7. Considering all the PDCCH candidates and twodifferent DCI lengths, total of 44 blind PDCCH decoding attempts may berequired in each subframe.

In addition to the FEC, error detection is used for PDCCH to enable theclient terminal to ensure whether the PDCCH decoding is successful ornot. The error detection is performed using a 16-bit Cyclic RedundancyCheck (“CRC”). The RNTI of the client terminal to which the PDCCH isaddressed is XOR-ed with the computed CRC over the DCI payload as shownin FIG. 8. The intended RNTI may be a broadcast RNTI or client terminalspecific RNTI.

During the course of blind PDCCH decoding the client terminal must matchthe locally computed CRC against one of the broadcast RNTIs or itsassigned unique RNTIs. Only when the XOR-ed CRC match, a PDCCH decodingis considered successful.

During blind PDCCH decoding in the client terminal, the input to thePDCCH decoder may be from an actual signal transmitted by eNB or fromsome random values from parts of the downlink signal. This may bebecause the eNB may not be transmitting any information at all or may betransmitting information intended for other client terminals. Only few(typically two or three) of the 44 blind decoding attempts may have auseful signal transmitted by eNB intended for the particular clientterminal as input to the PDCCH decoder. The probability that a random16-bit pattern matches the true CRC for the payload portion of the datais 1/2¹⁶. When a computed CRC on the received PDCCH matches the receivedCRC when there was no PDCCH transmitted, it is defined as a false PDCCHdecoding. Considering that there are 44 blind decoding attempts made bythe client terminal per subframe, the probability of getting a falsePDCCH decoding per subframe is 44*(1/2¹⁶). Furthermore, the PDCCH CRC ischecked in conjunction multiple RNTIs that may be used by the clientterminal. Assuming that on average two identifiers may be used by theclient terminal at any given time, the probability of false PDCCHdetection may be increased further by a factor of two, i.e.,2*44*(1/2¹⁶). Since there are 1000 subframes in one second, theprobability of getting one false PDCCH per second is 1000*2*44*(1/2¹⁶).This translates to about a 134% chance of one false PDCCH decoding persecond. This means that at least one false PDCCH is likely to occurevery second. When a UE is required to decode PDCCH with additionalRNTIs such as SI-RNTI or SPS-RNTI, the probability of false PDCCHdetection is further increased.

The false PDCCH decoding may lead to false DCI which in turn leads tofalse resource allocation in the client terminal. Such false PDCCHdetection may cause two types of problems. If the false PDCCH detectionis related to downlink resource allocation then it may cause the clientterminal to receive the downlink data that does not actually contain anyinformation for that particular client terminal. This results inunnecessary power consumption in the client terminal. Furthermore, ifthere was another allocation in the same subframe that was actuallyintended for the client terminal there may be conflict in the allocatedresources. This may cause the client terminal to behave in anunpredictable manner and could result in the client terminal notreceiving the data that was intended for it. For the uplink direction,the false detection of the PDCCH may result in the client terminaltransmitting on resources that are not granted to it. This may causeinterference to other client terminal which may be allocated thoseparticular resources. This may lead to unnecessary power consumption onall the client terminals that may be transmitting on those particularresources. Furthermore, the bandwidth is wasted in both the downlink andthe uplink of the wireless communication system.

The LTE wireless communication system uses Hybrid Automatic RepeatRequest (“HARQ”). False PDCCH detection can also cause the HARQ FiniteState Machine (“FSM”) running at the client terminal and at the eNB tobe out of sync. For each downlink resource allocation there is acorresponding HARQ acknowledgement in the uplink. The location of uplinkacknowledgement is based on the start position of the PDCCH blinddecoding candidate. The false PDCCH decoding then in turn leads totransmission of HARQ acknowledgment (positive or negative) in the uplinkdirection at the wrong location in uplink resources and possiblyinterfering with other client terminals that may be sending HARQacknowledgements. The false PDCCH decoding may lead to a series ofproblems that compound over a period of few subframes.

Multiple successful PDCCH detection may occur when single set of PDCCHdata is processed by the receiver in the client terminal assumingdifferent message sizes and coding rates and AL. For example, it may bepossible to successfully decode a message of the same size withdifferent AL assumption. This leads to multiple successful decoding of asingle PDCCH for a given client terminal. This is referred herein asduplicate PDCCH detection.

SUMMARY OF THE INVENTION

In accordance with aspects of the invention, a computer-implementedmethod of checking for false downlink control information in a wirelesscommunication system is provided. The method comprises selecting one ormore radio network temporary identifiers (RNTI) for which a physicaldownlink control channel (PDCCH) needs to be configured for a presentoperating mode of a client device; for every subframe, configuring, byone or more processors, the one or more selected RNTI into a PDCCHdecoder; for every subframe, configuring a number of PDCCHs to bereceived for each configured RNTI to the PDCCH decoder; and performingPDCCH decoding using the PDCCH decoder.

In one example, the method further comprises limiting a maximum numberof blind PDCCH decoding attempts based on an expected maximum number ofsuccessful PDCCHs in any given subframe. In another example, the methodfurther comprises, after performing the PDCCH decoding, determiningwhether a cyclic redundancy check (CRC) of the decoded PDCCH matches anyof the configured RNTI. Here, when the PDCCH CRC does not match with anyof the configured RNTI, the method may further comprise determiningwhether to continue further PDCCH decoding based on whether a maximumnumber of PDCCH decoding attempts has been completed. Alternatively,when the PDCCH CRC matches with one of the configured RNTI, the methodmay further comprise incrementing the number of PDCCH decoded for thematching RNTI. In this case, the method may further comprisesdetermining whether the configured number of PDCCHs for a given RNTI isdecoded or not; when the configured number of PDCCHs for a given RNTI isnot decoded yet, determining whether the maximum number of PDCCHdecoding attempts has been completed; and when the configured number ofPDCCHs for a given RNTI is decoded, removing from the list of configuredRNTIs for the current subframe the RNTI for which the configured numberof PDCCHs are decoded.

According to other aspects, a processing system configured to check forfalse downlink control information in a wireless communication networkis provided. The system comprises memory configured to store informationassociated with one or more radio network temporary identifiers (RNTI)and one or more physical downlink control channels (PDCCH), and one ormore processors. The processors are configured to select one or moreRNTI for which a PDCCH needs to be configured for a present operatingmode of a client device; for every subframe, configure the one or moreselected RNTI into a PDCCH decoder; for every subframe, configure anumber of PDCCHs to be received for each configured RNTI to the PDCCHdecoder; and perform PDCCH decoding using the PDCCH decoder.

In one example, the one or more processors are further configured to:determine whether a cyclic redundancy check (CRC) of the decoded PDCCHmatches any of the configured RNTI; when the PDCCH CRC does not matchwith any of the configured RNTI, determine whether to continue furtherPDCCH decoding based on whether a maximum number of PDCCH decodingattempts has been completed; and when the PDCCH CRC matches with one ofthe configured RNTI, incrementing the number of PDCCH decoded for thematching RNTI. In this case, the one or more processors may be furtherconfigured to: determine whether the configured number of PDCCHs for agiven RNTI is decoded or not; when the configured number of PDCCHs for agiven RNTI is not decoded yet, determine whether the maximum number ofPDCCH decoding attempts has been completed; and when the configurednumber of PDCCHs for a given RNTI is decoded, remove from the list ofconfigured RNTIs for the current subframe the RNTI for which theconfigured number of PDCCHs are decoded.

According to further aspects, a wireless communication device isconfigured to check for false downlink control information in a wirelesscommunication network. The device comprises a transceiver, memory, aPDCCH decoder, and one or more processors. The transceiver is configuredto receive downlink control information; memory configured to storeinformation associated with one or more radio network temporaryidentifiers (RNTI) and one or more physical downlink control channels.The PDCCH decoder is configured to perform PDCCH decoding. And the oneor more processors are operatively coupled to the transceiver, thememory and the PDCCH decoder. The one or more processors are configuredto: select one or more RNTI for which a PDCCH needs to be configured fora present operating mode of a client device; for every subframe,configure the one or more selected RNTI into the PDCCH decoder; forevery subframe, configure a number of PDCCHs to be received for eachconfigured RNTI to the PDCCH decoder; and cause the PDCCH decoder toperform the PDCCH decoding.

In accordance with other aspects, a computer-implemented method ofdetecting false downlink control information in a wireless communicationsystem is provided. The method comprises: determining, by one or moreprocessors, whether a physical downlink control channel (PDCCH)candidate has been successfully decoded at a first aggregation level ofa particular tree structure; when it is determined that the PDCCHcandidate has been successfully decoded at the first aggregation levelof the particular tree structure, skipping PDCCH candidates at a second,higher, aggregation level within the particular tree structure;performing, by the one or more processors, duplicate PDCCH detection;when the detection determines that the PDCCH candidate is not aduplicate, extracting a hybrid automatic repeat request (HARQ) processidentity from a downlink control information (DCI) message; anddetermining whether the HARQ process identity is within an expectedlimit.

In one example, when the detection determines that the PDCCH candidateis a duplicate, the method declares the PDCCH candidate a duplicate anddiscarding it. In another example, performing the duplicate PDCCHdetection includes checking whether a message is identical to anothersuccessfully decoded message of the same length. In a further example,performing the duplicate PDCCH detection includes checking whether acyclic redundancy check (CRC) of a decoded PDCCH message is identical tothe CRC of a previously decoded PDCCH message.

In yet another example, the method further comprises: extracting newdata indicator (NDI) and modulation and coding scheme (MCS) fields fromthe DCI message; determining whether the extracted NDI field has toggledcompared to an NDI value in a last received DCI for a same HARQ processidentity; and when it is determined that the extracted NDI field hastoggled, checking the value of the MCS field to determine whether itsatisfies a predetermined threshold such that the received DCI is a trueDCI. Here, the method may further comprise: when it is determined thatthe extracted NDI field has not toggled, determining whether theextracted MCS satisfies the predetermined threshold and whether any DCIfor the same HARQ process identity was previously received with the sameMCS value; and when the extracted MCS value and any DCI for the sameHARQ process identity was previously received with the same MCS value,identifying the received DCI as the true DCI.

In accordance with further aspects of the invention, a processing systemis configured to detect false downlink control information in a wirelesscommunication network. The system comprises: memory configured to storeinformation associated one or more physical downlink control channels(PDCCH) and one or more processors coupled to the memory. The one ormore processors are configured to: determine whether a PDCCH candidatehas been successfully decoded at a first aggregation level of aparticular tree structure; when it is determined that the PDCCHcandidate has been successfully decoded at the first aggregation levelof the particular tree structure, skip PDCCH candidates at a second,higher, aggregation level within the particular tree structure; performduplicate PDCCH detection; when the detection determines that the PDCCHcandidate is not a duplicate, extract a hybrid automatic repeat request(HARQ) process identity from a downlink control information (DCI)message; and determine whether the HARQ process identity is within anexpected limit.

In one example the one or more processors are further configured to:extract new data indicator (NDI) and modulation and coding scheme (MCS)fields from the DCI message; determine whether the extracted NDI fieldhas toggled compared to an NDI value in a last received DCI for a sameHARQ process identity; and when it is determined that the extracted NDIfield has toggled, check the value of the MCS field to determine whetherit satisfies a predetermined threshold such that the received DCI is atrue DCI. In this case, the one or more processors may be furtherconfigured to: when it is determined that the extracted NDI field hasnot toggled, determine whether the extracted MCS satisfies thepredetermined threshold and whether any DCI for the same HARQ processidentity was previously received with the same MCS value; and when theextracted MCS value and any DCI for the same HARQ process identity waspreviously received with the same MCS value, identify the received DCIas the true DCI.

And in accordance with yet another aspect, a wireless communicationdevice is configured to detect false downlink control information in awireless communication network. The device comprises a transceiverconfigured to receive downlink control information; memory configured tostore information associated with one or more physical downlink controlchannels (PDCCH); a PDCCH decoder configured to perform PDCCH decoding;and one or more processors operatively coupled to the transceiver, thememory and the PDCCH decoder. The one or more processors are configuredto: determine whether a PDCCH candidate has been successfully decoded ata first aggregation level of a particular tree structure; when it isdetermined that the PDCCH candidate has been successfully decoded at thefirst aggregation level of the particular tree structure, skip PDCCHcandidates at a second, higher, aggregation level within the particulartree structure; perform duplicate PDCCH detection; when the detectiondetermines that the PDCCH candidate is not a duplicate, extract a hybridautomatic repeat request (HARQ) process identity from a downlink controlinformation (DCI) message; and determine whether the HARQ processidentity is within an expected limit.

In one example, the one or more processors are further configured to:extract new data indicator (NDI) and modulation and coding scheme (MCS)fields from the DCI message; determine whether the extracted NDI fieldhas toggled compared to an NDI value in a last received DCI for a sameHARQ process identity; and when it is determined that the extracted NDIfield has toggled, check the value of the MCS field to determine whetherit satisfies a predetermined threshold such that the received DCI is atrue DCI. In this case, the one or more processors may be furtherconfigured to: when it is determined that the extracted NDI field hasnot toggled, determine whether the extracted MCS satisfies thepredetermined threshold and whether any DCI for the same HARQ processidentity was previously received with the same MCS value; and when theextracted MCS value and any DCI for the same HARQ process identity waspreviously received with the same MCS value, identify the received DCIas the true DCI.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a conventional cellular wireless communicationsystem.

FIG. 2 illustrates a conventional wireless communication system.

FIGS. 3 and 3A illustrate subframe level details for the air interfacestructure of the LTE wireless communication system.

FIG. 4 illustrates different Aggregation Levels for PDCCH in LTEwireless communication system.

FIG. 5 illustrates PDCCH candidate mapping to CCEs for Common SearchSpace illustrates.

FIG. 6 illustrates PDCCH candidate mapping to CCEs for UE SpecificSearch Space.

FIG. 7 summarizes the PDCCH Candidates per Search Space and AggregationLevel.

FIG. 8 illustrates the PDCCH CRC generation and XOR-ing with RNTI.

FIG. 9 lists the subframes in which DCI for UL allocation may occur.

FIG. 10 lists the simultaneous parallel reception type required for UEof the LTE wireless communication system.

FIGS. 11A-B illustrate the false PDCCH decoding detection and avoidanceaccording to an aspect of the present invention.

FIG. 12 lists the maximum number of HARQ processes for different (“TimeDivision Duplex”) TDD configurations.

FIGS. 13A-B illustrate the parsing of DCI for detection and avoidance offalse DCI according to an aspect of the present invention.

FIGS. 14A-B illustrate an example of checks to be performed for falseDCI detection according to an aspect of the present invention.

FIG. 15 illustrates a diagram of a wireless mobile station usable inaccordance with aspects of the present invention.

FIG. 16 illustrates a diagram of a baseband subsystem for a wirelessmobile station usable in accordance with aspects of the presentinvention.

FIG. 17 illustrates an RF subsystem for a wireless mobile stationdiagram.

DETAILED DESCRIPTION

Methods and apparatus are described that reduce the probability of falsePDCCH detection and duplicate PDCCH detection.

According to an aspect of the present invention, some false PDCCHdetections may be identified by checking the content of the decodedmessage. The PDCCH carries payloads of different DCI messages. Each ofthe DCI messages is transmitted according to a specific formatcomprising a number of bit fields. The output of the PDCCH decoder isparsed for the expected format. In one scenario, the following list ofchecks is performed for identifying the false PDCCH detection:

Checks to be Performed to Avoid False PDCCH before DCI Data Parsing

-   -   1. Only one SI-RNTI based PDCCH or P-RNTI based PDCCH may be        detected in a subframe.    -   2. Only one RA-RNTI or C-RNTI or SPS-C RNTI or Temp-C RNTI based        PDSCH is allowed in a subframe.    -   3. Only one PUSCH grant (DCI Format 0) based on C-RNTI, SPS-C        RNTI or Temp-C RNTI is allowed in a subframe. For TDD        Configuration 0, at most two grants, based on C-RNTI, SPS-C RNTI        or Temp-C RNTI, are allowed.    -   4. The protocol software is aware of the maximum number of        successful PDCCHs to be expected in any given subframe. This        information is used to limit the maximum number of blind PDCCH        decoding attempts.    -   5. In a TDD configuration, some subframes may never carry a UL        grant related DCI. In some TDD configurations, some subframes        may never carry DL allocation related DCI. This information is        controlled by limiting the number of decoded DCIS on a per        subframe basis according to the table contained in FIG. 9.        -   a. Maximum number of DL DCI matching with C-RNTI [possible            values 0, 1]        -   b. Maximum number of DL DCI matching with Temp-C RNTI            [possible values 0, 1]        -   c. Maximum number of UL DCI (DCI with Format 0) matching            with C-RNTI [possible values are 0, 1, 2]. The value of 2 is            only applicable in case of TDD duplexing scheme with TDD            Configuration-0.        -   d. Max DCI with Format 0 matching with Temp-C RNTI [possible            values are 0, 1]    -   6. The client terminal may need to use multiple identities,        i.e., RNTIs such as RA-RNTI, C-RNTI, SPS-C RNTI, Temp-C RNTI,        SI-RNTI, and P-RNTI. The CRC is checked after XOR-ing the        received CRC with only the expected RNTIs for any given subframe        based on the a priori information and the information exchanged        between the UE and eNB. For example, the timing of the        transmission of subframes with SI-RNTIs is known to the UE        partially before camping on to a cell and fully after camping on        to a cell.    -   7. Some RNTIs are only valid when the client terminal is in        certain modes. For example, the P-RNTI is valid only when the        client terminal is not having an active data connection with the        eNB. Therefore, the P-RNTI is enabled only when the client        terminal does not have an active data connection with the eNB.    -   8. Broadcast messages can only be transmitted by the eNB in the        common search of the blind PDCCH decoder. Therefore, any enabled        broadcast RNTI (SI-RNTI, P-RNTI, RA-RNTI, Temp-C-RNTI) are used        only when the decoded PDCCH candidate is from the CSS.    -   9. The LTE specifications 3GPP TS 36.302: “Evolved Universal        Terrestrial Radio Access (E-UTRA); Services provided by the        physical layer” defines a variety of Reception Types as shown in        table contained in FIG. 10. False DCI can be detected based on        DL Reception Type violations as follows:        -   a. Only one SI-RNTI based DCI is allowed in “Reception            Type-B”        -   b. Only one P-RNTI based DCI is allowed in “Reception            Type-C”        -   c. Only one DCI from “Reception Type D/E/G/I” are allowed        -   d. Only one DCI from “Reception Type F/H/J” are allowed in            FDD mode        -   e. One DCI from “Reception Type F/H/J” and one DCI from            “Reception Type H/J” are allowed in TDD mode.

The flow diagram contained FIGS. 11A-B illustrate an example of theprocessing steps for checks to be performed for false DCI before DCIdata parsing. The steps 1 through 9 described above are implemented atprocessing blocks 1102, 1104 and 1106 in FIG. 11A. The processing blocks1110, 1112, 1114, 1116, 1118, 1120 and 1122 in FIG. 11B implement thechecking of the received decoded PDCCH against the information generatedby the blocks in FIG. 11A as per steps 1 to 9 paragraph.

For each subframe, a determination is made in block 1102 about the RNTIsfor which PDCCH need to be performed for the present operating mode ofthe UE. This determination is made anew for every subframe. Once thedetermination is made in block 1102, the selected RNTIs are configuredinto the PDCCH decoder as shown in block 1104.

Next the number of PDCCHs to be received for each RNTI is configured tothe PDCCH decoder as shown in block 1106. Next the PDCCH decoding isstarted as shown in block 1108. At this point a decision made in block1110 as to whether the decoded PDCCH CRC matches with any of theconfigured RNTIs. If the PDCCH CRC does not match with any of theconfigured RNTIs, a decision is made in block 1112 whether to continuefurther PDCCH decoding. This decision is based on whether the maximumnumber of PDCCH decoding attempts has been completed or not. If themaximum number of PDCCH decoding attempts is completed, then theprocessing flow jumps to block 1114 and the PDCCH decoding for the givensubframe stops at that point. If the maximum number of PDCCH decodingattempts is not completed, then the processing flow returns to block1108.

Returning to block 1110, if the PDCCH CRC matches with one of theconfigured RNTIs, the number of PDCCH decoded for the matching RNTI isincremented in block 1116. At this point a check is performed in block1118 to determine whether the configured number of PDCCHs for a givenRNTI is decoded or not. If the configured number of PDCCHs for a givenRNTI is not decoded yet, the processing flow returns to block 1112.

If the configured number of PDCCHs for a given RNTI is decoded, the RNTIfor which the configured number of PDCCHs are decoded is removed fromthe list of configured RNTIs for the current subframe in block 1120 toeliminate it from further PDCCH decoding consideration.

Next a check is performed in block 1122 to determine whether aconfigured number of PDCCH for all configured RNTIs is received or not.If the configured number of PDCCH for all configured RNTIs is notreceived, the processing returns to block 1112. If the configured numberof PDCCH for all configured RNTIs is not received, the processingreturns to block 1112. If configured number of PDCCH for all configuredRNTIs is received, the processing goes to block 1114 and the PDCCHdecoding for the given subframe stops at that point.

Checks to be Done for False PDCCH after DCI Data Parsing

-   -   1. Duplicate DCI detection may be performed as follows:        -   a. The aggregation levels (AL) are defined as trees            structured such that the PDCCH candidates at lower            aggregation level are subset of PDCCH candidates at higher            aggregation level. If a PDCCH candidate is decoded            successfully at a lower aggregation level, candidates at            higher aggregation level within the same tree are skipped.            This may avoid possible duplicate DCI detection. This step            is implemented in block 1303 in FIG. 13A.        -   b. Duplicate PDCCH detection may be performed by checking            whether the message is identical to another successfully            decoded message of the same length. Note that it is possible            to have different messages of the same length; therefore            comparing the length alone may not be sufficient. Block 1304            in FIG. 13A implements this step.        -   c. Another method to avoid duplicate PDCCH detection is to            check whether the CRC of a decoded PDCCH message is            identical to the CRC of a previously decoded PDCCH. Block            1404 in FIG. 14A implements this step.    -   2. The number of HARQ processes for FDD mode is fixed to eight        whereas it varies for TDD based on the configuration type as        shown in table contained in FIG. 12. The DCIS with invalid HARQ        Process Identity for a given TDD Configuration may be used to        detect False DCI. This step is implemented in blocks 1308 and        1310 in FIG. 13A.    -   3. The New Data Indicator (“NDI”) field value compared to        previously received value for a given HARQ process must be        consistent with the Modulation and Coding Scheme (“MCS”) and        Redundancy Version (“RV”) fields of the DCI message.        Specifically, the initial transmission must not use the MCS and        RV values that correspond to retransmission. This step is        implemented by the blocks 1312, 1314, 1316, 1318, 1320 and 1322        as shown in FIG. 13B.

The flowchart contained in FIGS. 13A-B illustrates an example of theprocessing steps for checks to be performed for false DCI detection. Theprocessing flow starts at block 1302.

In block 1304 a determination is made as to whether the decoded PDCCHCRC matches with any of the previously decoded PDCCH CRC. If the decodedPDCCH CRC matches with any of the previously decoded PDCCH CRC, then theprocessing jumps to block 1306 where the newly decoded PDCCH isdetermined to be duplicate of previously decoded PDCCH and it isdiscarded.

Returning to block 1304, if the decoded PDCCH CRC does not match withany of the previously decoded PDCCH CRC, the HARQ process ID field isextracted from the DCI payload from the decoded PDCCH. Next, in block1310 a determination is made whether the extracted HARQ process ID iswithin the expected limits according to the table contained in FIG. 12.

If the extracted HARQ process ID is not within the expected limitsaccording to the table contained in FIG. 12, the DCI is determined to bea false DCI in block 1312 and it is discarded. Returning to block 1310,if the extracted HARQ process ID is within the expected limits accordingto the table contained in FIG. 12, the processing continues in block1314 where the NDI and MCS fields are extracted from the DCI message.

Next in block 1316, a determination is made whether the extracted NDI,which is a one bit field, has toggled compared to the NDI value in alast received DCI for the same HARQ Process ID. If the NDI value hastoggled, in block 1318 the value of the MCS field is checked todetermine whether it is less than 29 to ensure that the requiredinformation for a new transmission is available. If the MCS field isless than 29, the received DCI may be determined as true DCI in block1320. If the MCS field is greater than or equal to 29, the received DCImay be determined as false DCI in block 1320. Returning to block 1316,if the NDI value has not toggled, a determination is made in block 1322whether the extracted MCS≧29 and if so whether any DCI for the same HARQprocess ID was previously received with MCS<29. If the extracted MCS≧29and a DCI for the same HARQ process ID was previously received withMCS<29, the received DCI is determined to be a true DCI in block 1320.Otherwise, the received DCI is determined to be a false DCI in block1312.

The flowchart contained in FIGS. 14A-B illustrates an example of theprocessing steps for checks to be performed for false DCI detection. Theprocessing flow starts at block 1402 and follows similar processingsteps as in FIGS. 13A-B, but the function of duplicate DCI detectionblock 1304 is achieved in block 1404 using an alternate method describedin step 1 c above.

The above methods can be used independently or jointly to reduce thefalse and duplicate PDCCH detection probability.

By way of example only, the above-described example methods may beimplemented in a receiver, e.g., a user device such as a wireless mobilestation (“MS”) 12 as shown in FIG. 1.

As shown in FIG. 15, MS 100 may include a baseband subsystem 102 and aradio frequency (“RF”) subsystem 104 for use with a wirelesscommunication network. A display/user interface 106 provides informationto and receives input from the user. By way of example, the userinterface may include one or more actuators, a speaker and a microphone.

The baseband subsystem 102 and a RF subsystem 104 may be high speedserial communication devices communicating through the high speedcommunication link.

The baseband subsystem 102 as shown in FIG. 16 may include a controller108 such as a microcontroller or other processor. The RF subsystem 104as shown in FIG. 17 may include a controller 108 such as amicrocontroller or other processor. The controller 108 desirably handlesoverall operation of the MS 100, including management of the RFsubsystem 104. This may be done by software or firmware running on thecontroller 108. Such software/firmware may embody any methods inaccordance with aspects of the present invention.

A signal processor 110 may be used to process samples from the RFsubsystem 104 or other information sent or received by the MS 100. Thesignal processor 110 may be a stand-alone component or may be part ofthe controller 108. Memory 112 may be shared by or reserved solely forone or both of the controller 108 and the signal processor 110. Forinstance, signal processing algorithms may be stored in a non-volatilesection of memory 112 while coefficients and other data parameters maybe stored in RAM. Peripherals 114 such as a full or partial keyboard,video or still image display, audio interface, etc may be employed andmanaged through the controller 108.

The RF subsystem 104 preferably provides two-way communicationoperation. It may include one or more receivers/receive chains, atransmitter, a synthesizer, a power amplifier, and one or more antennasoperatively coupled together to enable communication. The receivechain(s) is operable to receive signals from one or more channels in awireless communication network. A signal processor 120 may be used toprocess samples from the baseband subsystem 102. The signal processor120 may be a stand-alone component or may be part of the controller 128.Memory 122 may be shared by or reserved solely for one or both of thecontroller 128 and the signal processor 120. For instance, signalprocessing algorithms may be stored in a non-volatile section of memory122 while coefficients and other data parameters may be stored in RAM.

Aspects of the present invention may be implemented in firmware of thesignal processor 110 and/or the controller 108 of the basebandsubsystem. In another alternative, aspects of the present invention mayalso be implemented as a combination of firmware and hardware of thebaseband subsystem. For instance, a signal processing entity of any orall of the FIG. 16 may be implemented in firmware, hardware and/orsoftware. It may be part of the baseband subsystem, the receiversubsystem or be associated with both subsystems. In one example, thecontroller 108 and/or the signal processor 110 may include or controlthe protocol entity circuitry. The software may reside in internal orexternal memory and any data may be stored in such memory. The hardwaremay be an application specific integrated circuit (“ASIC”), fieldprogrammable gate array (“FPGA”), discrete logic components or anycombination of such devices. The terms controller and processor are usedinterchangeably herein.

Aspects of the present invention may also be implemented in firmware ofthe signal processor 120 and/or the controller 128 of the RF subsystem104. In another alternative, aspects of the present invention may alsobe implemented as a combination of firmware and hardware of the RFsubsystem. For instance, a signal processing entity of any or all of theFIG. 17 may be implemented in firmware, hardware and/or software. Thesoftware may reside in internal or external memory and any data may bestored in such memory. The hardware may be an ASIC, FPGA, discrete logiccomponents or any combination of such devices.

Although aspects of the invention herein have been described withreference to particular embodiments, it is to be understood that theseembodiments are merely illustrative of the principles and applicationsof the present invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims. Aspects ofeach embodiment may be employed in the other embodiments describedherein.

The invention claimed is:
 1. A computer-implemented method of checkingfor false downlink control information in a wireless communicationsystem, the method comprising: selecting one or more radio networktemporary identifiers (RNTI) for which a physical downlink controlchannel (PDCCH) needs to be configured, based on an operating mode inwhich a client device is presently operating; for every subframe,configuring, by one or more processors, the one or more selected RNTIinto a PDCCH decoder; for every subframe, configuring a number of PDCCHsto be received for each configured RNTI to the PDCCH decoder; andperforming PDCCH decoding using the PDCCH decoder; and limiting amaximum number of blind PDCCH decoding attempts for a given selectedRNTI, based on a result of a determination whether a predeterminedmaximum number of successful PDCCHs in any given subframe for the givenselected RNTI is reached.
 2. The method of claim 1, further comprising,after performing the PDCCH decoding, determining whether a cyclicredundancy check (CRC) of the decoded PDCCH matches any of theconfigured RNTI.
 3. The method of claim 2, wherein, when the PDCCH CRCdoes not match with any of the configured RNTI, the method furthercomprises determining whether to continue further PDCCH decoding basedon whether a maximum number of PDCCH decoding attempts has beencompleted.
 4. The method of claim 2, wherein, when the PDCCH CRC matcheswith one of the configured RNTI, the method further comprisesincrementing the number of PDCCH decoded for the matching RNTI.
 5. Themethod of claim 4, further comprising: determining whether theconfigured number of PDCCHs for a given RNTI is decoded or not; when theconfigured number of PDCCHs for a given RNTI is not decoded yet,determining whether the maximum number of PDCCH decoding attempts hasbeen completed; and when the configured number of PDCCHs for a givenRNTI is decoded, removing from the list of configured RNTIs for thecurrent subframe the RNTI for which the configured number of PDCCHs aredecoded.
 6. A processing system configured to check for false downlinkcontrol information in a wireless communication network, the systemcomprising: memory configured to store information associated with oneor more radio network temporary identifiers (RNTI) and one or morephysical downlink control channels (PDCCH); and one or more processorsconfigured to: select one or more RNTI for which a PDCCH needs to beconfigured for a present operating mode of a client device; for everysubframe, configure the one or more selected RNTI into a PDCCH decoder;for every subframe, configure a number of PDCCHs to be received for eachconfigured RNTI to the PDCCH decoder; perform PDCCH decoding using thePDCCH decoder; and limit a maximum number of blind PDCCH decodingattempts for a given selected RNTI, based on a result of a determinationwhether a predetermined maximum number of successful PDCCHs in any givensubframe for the given selected RNTI is reached.
 7. The processingsystem of claim 6, wherein the one or more processors are furtherconfigured to: determine whether a cyclic redundancy check (CRC) of thedecoded PDCCH matches any of the configured RNTI; when the PDCCH CRCdoes not match with any of the configured RNTI, determine whether tocontinue further PDCCH decoding based on whether a maximum number ofPDCCH decoding attempts has been completed; and when the PDCCH CRCmatches with one of the configured RNTI, incrementing the number ofPDCCH decoded for the matching RNTI.
 8. The processing system of claim7, wherein the one or more processors are further configured to:determine whether the configured number of PDCCHs for a given RNTI isdecoded or not; when the configured number of PDCCHs for a given RNTI isnot decoded yet, determine whether the maximum number of PDCCH decodingattempts has been completed; and when the configured number of PDCCHsfor a given RNTI is decoded, remove from the list of configured RNTIsfor the current subframe the RNTI for which the configured number ofPDCCHs are decoded.
 9. A wireless communication device configured tocheck for false downlink control information in a wireless communicationnetwork, the device comprising: a transceiver configured to receivedownlink control information; memory configured to store informationassociated with one or more radio network temporary identifiers (RNTI)and one or more physical downlink control channels (PDCCH); a PDCCHdecoder configured to perform PDCCH decoding; and one or more processorsoperatively coupled to the transceiver, the memory and the PDCCHdecoder, the one or more processors being configured to: select one ormore RNTI for which a PDCCH needs to be configured, based on anoperating mode in which a client device is presently operating; forevery subframe, configure the one or more selected RNTI into the PDCCHdecoder; for every subframe, configure a number of PDCCHs to be receivedfor each configured RNTI to the PDCCH decoder; cause the PDCCH decoderto perform the PDCCH decoding; and limit a maximum number of blind PDCCHdecoding attempts for a given selected RNTI, based on a result of adetermination whether a predetermined maximum number of successfulPDCCHs in any given subframe for the given selected RNTI is reached.